Known in the art are processes for producing fibrides which are based on effluence of viscous solutions of polymers into a settler at a shear stress created, for example, by stirring (cf. U.S. Pat. No. 2,988,782, 1961; U.S. Pat. No. 3,068,527, 1962; British Pat. No. 959,743, 1964; Australian Pat. No. 261,184, 1965, USSR Inventor's Certificate No. 256154, 1969, Cl. D 01 F 6/00).
These prior art processes have disadvantages residing in their multi-stage character and the necessity of using large quantities of organic solvents and settling agents.
Known in the art is a process for producing fibrides in the course of synthesis of polymers under foam conditions with the supply of the monomer in the liquid phase, for example hexamethylenediamine, directly into the reaction zone of the reactor. The gas flow carried by air containing the monomer, for example terephthalic acid dichloroanhydride, is fed in an aerosol state into the reaction zone from the bottom. When the reacting phases contact, there occur chemical processes of polycondensation and neutralization of the evolving low-molecular weight substance, for example hydrogen chloride. Besides, in a highly turbulent reaction mass converted, by the kinetic head of the gas phase, to a mobile three-phase foam, the process of fibride-formation occurs to a certain extent, due to stretching of the resulting gel-like film of the polymer by the above-mentioned gas flow. The reaction mass containing: the synthetized polymer of a broad particle size and particle shapes, common salt as the product of neutralization of the low-molecular substance; water; an excess of hexamethylene and alkali; air is moved along the reactor towards the separation zone in the vertical plane following a complicated path. After the separation zone, the inert air saturated with vapors of the liquid phase is delivered to cooling and then exhausted into the atmosphere. The aqueo-alkaline suspension of the polymer after separation is subjected to filtration. The filtrate is recycled to the process with the view to utilize a excessive diamine, while the polymeric fibrides are washed, squeezed and packed (see the Report of the Kalinin Polytechnical Institute No. 7403815 "Process for the synthesis of polymers under foam-formation conditions", 1975, p. 36, deposited in VINITI, state registration No. 74035815, inv. No. 466424, 23.02.76).
This prior art process has disadvantages residing in a low yield of fibrides not exceeding 50-60%, their small size, insufficient molecular weight, non-uniformity of the polymer relative to the molecular weight and particle size, complexity of the process flow-sheet and difficulties of conducting the same under continuous conditions. Furthermore, the apparatus employed in the process necessitates additional means for fractionation of the product.
Also known is a process for producing polyamide fibrides by way of gas-liquid interphase polycondensation of haloanhydrides of dicarboxylic acids with bifunctional compounds (cf. USSR Inventor's Certificate No. 632766 of July 21, 1978). In this process the formation of fibrides occurs simultaneously with the synthesis of the polyamide from the monomers passing into the reaction zone in the liquid and gas phases. The gas stream containing the monomer such as terephthalic acid dichloroanhydride is passed, in the aerosol state from the stage of generation of the gas phase, into the reaction zone of the reactor through a perforated partition provided in the reactor between the zone of generation and the reaction zone; the free cross-section of the partition being equal to 25%. This gas stream is contacted with the liquid phase containing the monomer, for example hexamethylenediamine, supplied in the form of small drops by means of a mechanical nozzle positioned along the reactor axis above the aforementioned perforated partition. In the counter-current contacting phases there occurs, due to high kinetic energy of the gas stream, a phase inversion and the formation of a highly-turbulent layer of a movable foam having a highly-developed surface area whereupon chemical reactions of polycondensation and neutralization of the evolving hydrogen halide take place. At the same time, in the foam layer due to shear forces there occurs the formation of fibrides which are delivered, along with the reaction mass, by means of the kinetic gas stream to the zone of separation and defoaming, whereafter at the outlet of this zone they are subjected to filtration, washing, squeezing and packing.
However, the known process for producing fibrides with the nozzle-dropwise distribution of the liquid phase has certain disadvantages complicating operation of the apparatus and impairing quality characteristics of the product. The absence of the total overlapping of the cross-section of the reaction space by a continuous film part of the jet upon dropwise distribution creates non-uniformity of distribution of the liquid phase, local "breakthrough" of the monomer from the gas phase, decrease of the yield and molecular mass of the polymer. The aerosol state of the gas phase monomer does not provide for a uniform concentration of the monomer and strict equimolarity of the monomers in the reaction zone.
Known in the art are apparatus for physico-chemical and heat-exchange processes comprising a housing with a horizontal perforated partition, inlet pipe or a throttle valve for the supply of the starting components into the reaction zone, the outlet pipe for the discharge of the gas phase, as well as receiving and draining boxes for the liquid phase (see in book "Foam Conditions and Foam Apparatus", ed. by prof. I. P. Mukhlenov and prof. E. Ya. Tarat, Leningrad, "Khimija" Publishing House, 1977, pp. 16-20).
In the known apparatus there are no means ensuring the possibility for carrying out polycondensation processes, i.e. there is lack of an assembly creating conditions for generating a gas phase, regular distribution of the liquid phase, thus eliminating the use of liquid and solid monomers under normal conditions in the gas phase to obtain fibrides.
Known is an apparatus for the synthesis of polymers by the gas-phase polycondensation method which consists of three units: gas-phase generator and a reaction chamber partitioned by means of a perforated wall with the live cross-section of 25%, and a centrifuge foam suppressor. The diameter of the reaction chamber and evaporator of the gas-phase generation unit is 100 mm. To introduce the liquid phase and remove the polymer suspension, the reaction chamber is provided with corresponding pipes mounted in its side walls. Compensation of heat losses is ensured by means of a heating mantle provided at the outer surface of the reactor (cf. Report of the Kalinin Polytechnical Institute No. 74035815 "Process for the Synthesis of Polymers by the Method of Polycondensation under Foam-Formation Conditions", 1975, pp. 48-55, deposited in VINITI on Feb. 25, 1975, state registration No. 74035815, entry No. B 383154). However, due to the specific character of distribution of the liquid phase over the cross-section of the reactor over the partition this prior art apparatus has certain disadvantages. The polymer produced in this apparatus has a structural non-uniformity, contains a substantial portion of a low-molecular powder-like fractions, and features a relatively low average molecular weight and a small yield of fibrides. When the apparatus operation is stopped, the polymer suspension accumulated in the expander of the foam depressor drops through the perforated partition, contaminates the throttle valve and nozzle of the unit for the gas-phase generation, thus necessitating labor-consuming operations of dismantling and cleaning of the apparatus and increasing operating costs of the plant as a whole.
Also known are diffuser-foam apparatus containing no partitions and intended for carrying out the processes of heat and mass transfer under highly turbulent conditions. Such apparatus has a vertical conically-shaped diffuser with a narrow neck, whereinto gas is fed. The spraying liquid is introduced into the upper enlarged section of the diffuser. The advantage of the apparatus resides in the absence of clogging with dust (cf. in book "Foam Conditions and Foam Apparatus", ed. by prof. I. P. Mukhlenov and prof. E. Ya. Tarat, Leningrad, "Khimija" Publishers, 1977, p. 234).
However, this prior art design of the apparatus does not make it possible to carry out chemical processes of polycondensation in an intensive hydrodynamic stream to produce fibrides.
It is an object of the present invention to provide such a process which would ensure a full formation of a synthetic polymer to fibrides with an increased molecular mass and the same particle size over the entire cross-section of the reaction zone.
It is another object of the present invention to provide such a process for producing fibrides of synthetic heterochain polymers which would make it possible to simplify filtration of the suspension of the obtained product and washing of the polymer.
It is still another object of the present invention to provide such an apparatus for carrying out the process for producing fibrides of synthetic heterochain polymers which would make it possible to increase the efficiency of utilization of the working space of the reaction zone of the apparatus.
It is a further object of the present invention to provide such an apparatus for carrying out the process for producing fibrides of synthetic heterochain polymers which would make it possible to eliminate exhaust of pollutants into the environment.